The present invention relates to catheters for medical diagnostic or therapeutic use. In particular, the present invention relates to microcatheters of the type particularly adapted for navigating tortuous pathways in soft tissues, such as the brain.
A wide variety of catheters have been developed, for percutaneous insertion into the vascular system to accomplish any of a number of diagnostic or therapeutic objectives. For example, a wide variety of balloon dilatation catheters adapted for percutaneous transluminal coronary angioplasty are known. Peripheral vascular dilatation catheters, angiography catheters, drug delivery catheters and others are well represented in the prior art.
However, due to the relatively large diameter and minimal tortuosity of the peripheral vasculature and, to a lesser extent, the coronary vasculature, the prior art catheters are typically unsuited for use in the small tortuous vessels, such as those found in the soft tissue of the brain and liver. In addition to size constraints imposed by such soft tissue vasculature, catheters suitable for these applications must also exhibit optimal flexibility, while at the same time maintaining adequate column strength and other desirable properties. In general, the known catheters for one reason or another are unsuited for intercranial catheterizations. Such catheterizations are useful for a variety of diagnostic and interventional neurological techniques including drug delivery, imaging, treatment of aneurysms, tumors, arteriovenous malformations, and the like.
For example, in angiography, catheters are designed to deliver a radio-opaque agent to a target site within a blood vessel, to allow radiographic viewing of the vessel and blood flow characteristics near the release site. For the treatment of localized disease, such as solid tumors, catheters allow a therapeutic agent to be delivered to the target site at a relatively high concentration, with minimum overall side effects. Methods for producing localized vaso-occlusion in target tissue regions, by catheter injection of a vaso-occlusive agent, have also been described.
Often the target site which one wishes to access by catheter is buried within a soft tissue, such as brain or liver, and is only reached by a tortuous route through vessels or ducts typically having less than about a 3 mm lumen diameter. The difficulty in accessing such regions is that the catheter must be quite flexible, in order to follow the tortuous path into the tissue and, at the same time, stiff enough to allow the distal end of the catheter to be manipulated from an external access site, which may be as much as a meter or more from the target site.
Two general methods for accessing such tortuous-path regions have been devised. The first method employs a highly flexible catheter having a inflatable, but pre-punctured balloon at its distal end. In use, the balloon is partially inflated, and carried by blood flow into the target site. The balloon is continually inflated during placement to replenish fluid leaking from the balloon. A major limitation of this method is that the catheter will travel in the path of highest blood flow rate, so many target sites with low blood flow rates cannot be accessed.
In the second prior art method, a torqueable guide wire having a distal bend is guided, by alternatively rotating and advancing the wire, to the target site. With the wire in place, the catheter is then advanced along the wire until the distal catheter is then advanced along the wire until the distal catheter end is positioned at the target site. An important advantage of this method is the ability to control the location of the catheter along a tortuous path. Torqueable guide wires which can be guided into delicate, tortuous, and narrow vasculature are available. However, it is often difficult or impossible to advance a catheter over the wire, especially where the wire extends along a tortuous path of more than about 10 cm. If the catheter is relatively rigid, it cannot track over the final distal portion of the wire in the tortuous path region, because catheter advancement buckles the wire in a narrow turn, or because catheter advancement pulls the wire out of the distal vessels. On the other hand, catheters having more flexible shafts, such as those used in balloon flow-directed devices, lack the column strength in the catheter's proximal section to be advanced over the guide wire without buckling.
The need in the art for suitably flexible and small diameter medical catheters is exemplified by the statistical prevalence of vascular disorders of the brain associated with stroke. Stroke is currently the third leading cause of death in the United States with an estimated annual cost of $30 billion. In the United States alone, stroke affects in excess of 500,000 Americans annually, resulting in 150,000 deaths. Current treatment options are relatively limited and generally highly invasive.
Thus, there remains a need in the art for the development of catheters useful in minimally invasive procedures to diagnose and treat vascular diseases of the brain, such as those associated with stroke, and other diseased sites accessible through only the small vessels of the circulatory system.